Domain: Mike Mentzer's Heavy Duty

hito is a Heavy Duty training tracker.

Source of doctrine: `doc/Mike_Mentzer_Heavy_Duty_I.md` (HD1). Every domain decision must be justified against it. - It is copyrighted local reference material, gitignored, and never committed.
On conflict between a design choice and the doctrine: 1. The doctrine wins, or 2. The conflict is raised explicitly.

Principles that bind the model

**Intensity is categorical, not scalar.** - A working set is taken to momentary muscular failure; that *is* its definition (HD1, "The Intensity Factor": the only accurate measures are 0% at rest and 100% at failure). - Going further is qualitative — `Beyond_failure`: forced reps, negatives, rest-pause, static hold. - Never introduce a numeric "intensity score".
**Recovery produces growth; the gym only stimulates it.** - Stimulation is immediate; production is not (HD1, "The Economics of Growth and Recovery": recovery precedes growth). - Recovery is systemic and time-based — any hard workout gates the next one.
**Volume beyond the minimum is harmful.** - One working set per exercise is nominal; three sets per muscle is the ceiling. - The net negative effect of each extra set increases geometrically. - Rising volume is a diagnostic warning — never an achievement or a progress target.
**Progressive overload is the progress signal.** - Progress = an increase in reps, weight, or both; one extra rep counts. - Reps are an *outcome*, never a target — a set ends at failure, not at a number. The prescribed band only calibrates load. - Raise the load once twelve reps are reached, by 10-20%, so failure returns inside the band. - Note the slack: a 6-10 band is not breached at eleven.
**Brief, infrequent, intense.** - Shorter sessions at equal or better overload are favourable.
**Focus over novelty.** - Exercises come from a curated catalog. - Substitutions are limited to author-specified whitelists, which a routine may only narrow.

Encoding rules

Prefer making an illegal training state unrepresentable over validating it at runtime.
Deviations from doctrine (training early, extra volume) must be *possible* but never *silent*: - Require an explicit acknowledgement. - Retain that acknowledgement.
Keep plan and record distinct: - Prescription/routine vs logged workout. - Prescription vs progression (plan vs observation).
The logbook records; it never interprets. - Judgement belongs to one module. - Invariants belong on plans, which are authored — not on history, which is observed. - A log that refuses to state what happened is worse than one recording an error.
On a stall, the answer is never more work. - No remedy may add volume or frequency. - Doctrinal remedy (HD1, "Regulating Volume and Frequency"): after two weeks of no progress, take a week off, then *reduce* volume and frequency — drop sets and add rest days.